Dynamic spin response of a strongly interacting Fermi gas

TL;DR

This paper experimentally investigates the dynamic spin response of a strongly interacting Fermi gas using Bragg spectroscopy, revealing spin suppression at low energies and a universal high-frequency tail at high momentum.

Contribution

It provides the first independent measurements of spin-parallel and spin-antiparallel structure factors in a strongly interacting Fermi gas.

Findings

Spin response is suppressed at low energies due to pairing.

Density response is enhanced at low energies.

Spin-antiparallel dynamic structure factor exhibits a universal tail proportional to ω^{-5/2}.

Abstract

We present an experimental investigation of the dynamic spin response of a strongly interacting Fermi gas using Bragg spectroscopy. By varying the detuning of the Bragg lasers, we show that it is possible to measure the response in the spin and density channels separately. At low Bragg energies, the spin response is suppressed due to pairing, whereas the density response is enhanced. These experiments provide the first independent measurements of the spin-parallel and spin-antiparallel dynamic and static structure factors and open the way to a complete study of the structure factors at any momentum. At high momentum the spin-antiparallel dynamic structure factor displays a universal high frequency tail, proportional to $\omega^{-5/2}$, where $\hbar \omega$ is the probe energy.